High-power circuits dissipate a significant fraction of its power in the form of heat. The temperature of a circuit depends upon the heat generating characteristics of the circuit components, the heat transfer properties of the circuit package, and the temperature of the surrounding environment. As the temperature of a circuit component approaches the operating temperature limit, the performance of the circuit component substantially degrades. More specifically, operating a circuit at high temperatures reduces its operating life-span, causes it to operate at slower speeds, and causes it to produce other non-ideal operating characteristics. As can be appreciated by one of ordinary skill in the art, the operating temperature of a circuit can be reduced by enhancing the heat dissipation properties of a circuit package housing the circuit.
As known by one of ordinary skill in the art, heat dissipation from circuit packages can be enhanced by the use of externally mounted metallic heat sinks. One example of a circuit package utilizing an attached heat sink is shown in U.S. Pat. No. 5,517,058, to Temple. Heat sinks such as those disclosed in Temple are typically made of aluminum or aluminum alloy and are attached to the top surface of a molded plastic circuit package by mechanical means and/or with a thermally conductive adhesive.
Although externally mounted heat sinks may enhance the heat dissipation of a circuit package, external heat sinks are not suitable for many applications. For instance, in circuit designs where circuit packages are closely aligned or enclosed in a small housing, external heat sinks complicate design efforts and often result in added cost and wasted space. External heat sinks also present many other design complications because they substantially increase the dimensions and weight of a circuit package.
As also known in the art, heat dissipation from a circuit package may also be increased by the use of a material having suitable heat transfer properties. For instance, as shown in European Patent EP 0767495B1 to Sono et al., the bulk of a circuit package consists of a resin. In such designs, the heat dissipated by the circuit component encapsulated in the resin may be enhanced by providing additional thermal pathways from the individual circuit components to the external environment. Although these generally known designs may enhance heat dissipation of a circuit package, such designs also rely on a heat sink to draw the generated heat away from the circuit components and circuit package itself. Such prior art circuit packages present design complications similar to those described above.
As summarized above, is can be appreciated by one of ordinary skill in the art that there is a need for a circuit package with improved heat dissipation properties, and a design that consumes less space.